The present invention relates to diffraction devices used in optical systems and devices, and more particularly to a volume-phase holographic diffraction device designed for performance in short-wavelength (i.e., ultraviolet) spectral regions.
Optical sensors often rely on information gathered from certain bands of light reflected or scattered from a material or object under investigation. In particular, energy associated with Raman scattering in the ultraviolet (UV) spectral region may be of interest in identifying certain materials. Because of the intrinsically weak nature of the signals on which these devices operate, the devices used to detect these weak signals should be as optically efficient as possible. Moreover, in a spectrograph, the light dispersion element (in many cases, a diffraction grating), is the major source of light loss. Other surfaces used to direct or otherwise modify the incoming signal add to the noise (from scattering) and attenuate the strength of the optical beam (from absorption). Thus, it is desirable to optimize the efficiency of each component in the spectrograph, and in particular the efficiency of the diffraction grating.
Another important factor in the design of an optical element, such as a diffraction grating, is its aging parameters. The materials used in fabricating the diffraction grating may break down over time from exposure to light, and may do so faster if the material interacts with the light in certain ways.
Conventional design philosophy for volume-phase holographic diffraction gratings has been that a gelatin material would not be suitable for a grating that is to operate on very short wavelengths of light. Many experts in the field believe that the gelatin material would absorb too much of the incoming light (and would thus be unsuitable in this wavelength regime) and would decay quickly. To the contrary, it has been discovered and as presented hereinafter, that a diffraction grating using a gelatin material can be optimized for operation on short wavelength light, such as light in the UV spectral region.